Mostly I'm peeking at PLC (Programmable Logic Controller) values via various DDE/OPC comms drivers, several are used, but the most common is called RSLinx, from Rockwell Software (Allen-Bradley PLCs).
There are an increasing number of times it would be useful to reverse the data-flow direction, i.e. be able to input data into Excel, and get this to 'write' the data to the external application or database. I know for sure RSLinx is not where the problem lie.
My problem is the basic principles involved in getting Excel to accept data input into a cell, firstly without overwriting the formula (the external refernece) in it, and secondly, how to set Excel up to write-out data.
Without being too specific about the external drivers, or the other applications, all I need help with is how to hook-up a bidirectional DDE link in Excel, and providing it's DDE or OPC enabled, it should work with any DDE/OPC driver/application, shouldn't it? I thought thats what DDE was all about - seamless data exchange.